1. Field Of The Invention
This invention relates to the infrared soldering of components on circuit boards by infrared radiation, and in particular to the infrared soldering of surface mounted components. More specifically, the invention is concerned with the infrared soldering of components, and in particular surface mounted components, on one surface of a circuit board after other components have been mounted on the other surface of the circuit board.
2. Related Art
Circuit boards very frequently have components on both surfaces of the board. Thus, for example, a circuit pattern will be formed on one surface, with contact pads at various positions. Holes are provided through the board, aligned with some of the pads. In a first step, leaded components are mounted on the surface remote from the circuit pattern via leads passed through the holes and soldered to pads. Such soldering is usually done by wave soldering, although other forms of soldering can be used. Following soldering of the leads, in a further step, other components, and in particular surface mounting components, are mounted on the surface of the board on which is formed the circuit pattern. The soldering of these other components is performed by various methods, one of which is by infrared irradiation.
A basic problem relating to the soldering of the components in the further step is obtaining satisfactory fusion or melting of the solder paste while at the same time avoiding melting of other solder joints, such as the solder attaching leaded components, which will be hanging down from what would be the lower surface of the board when the surface mounting components are being soldered. Even if a solder of lower melting point is used in the second step, for the surface mounted and any other components, a fully satisfactory solution is not achieved.
A further problem is that during heating of a circuit board prior to soldering the other components, the previously soldered components can be heated to a temperature which can cause malfunction of the components or lead to a reduced operating life.
Various other problems exist in the process of mounting surface mounted components on boards to which other components have been mounted.